Microelectronic component assemblies and microelectronic component lead frame structures

ABSTRACT

The present invention provides microelectronic component assemblies and lead frame structures that may be useful in such assemblies. For example, one such lead frame structure may include a set of leads extending in a first direction and a dam bar. Each of the leads may have an outer length and an outer edge. The dam bar may include a plurality of dam bar elements, with each dam bar element being joined to the outer lengths of two adjacent leads. In this example, each dam bar element has an outer edge that extends farther outwardly than the outer edges of the two adjacent leads. The outer edges of the leads and the outer edges of the dam bar elements together define an irregular outer edge of the dam bar. Other lead frame structures and various microelectronic component assemblies are also shown and described.

BACKGROUND

The present invention relates to packaged microelectronic components andmethods for assembling the same. In particular, aspects of the inventionrelate to microelectronic component lead frame structures and to stackedmicroelectronic component assemblies.

Semiconductor chips or dies are typically encapsulated in a package thatprotects the chips from the surrounding environment. The packagestypically include leads or other connection points that allow theencapsulated chip to be electrically coupled to another microelectroniccomponent. Leaded packages include a semiconductor chip bonded to a leadframe either seated on a die paddle or directly to the leads, e.g., in aleads-over-chip attachment. The contacts pads on the semiconductor dieare then electrically connected to the chip, e.g., by wire bonding. Theconnected lead frame and chip may then be encapsulated in a moldcompound to complete the microelectronic component package. In mostcommon applications, the leads extend out from the mold compound,allowing the chip to be electrically accessed. Typically, the leadsextend laterally outwardly in a flat array that is part of a lead frame.This lead frame may be trimmed and formed into a desired configuration.

One increasingly popular technique for maximizing device density on asubstrate is to stack microelectronic devices on top of one another.Stacking just one device on top of a lower device can effectively doublethe circuitry within a given footprint; stacking additional devices canfurther increase the circuit density. In one approach, individualmicroelectronic components, e.g., individual semiconductor dies, areseparately packaged. These separate packages are then stacked atop oneanother to form a multi-package assembly. Such an approach isillustrated in PCT International Publication Number WO99/65062, theentirety of which is incorporated herein by reference.

In an alternative approach, multiple microelectronic components areassembled in a single package. FIGS. 1-5 schematically illustrate a thinsmall outline package (TSOP) 10 that includes an upper microelectroniccomponent 20 and a lower microelectronic component 30. Typically, thesemicroelectronic components are semiconductor dies. Leads 42 of an upperlead frame 40 may be physically attached to the upper microelectroniccomponent 20 via an adhesive, such as a conventional lead-on-chip tape.The inner lengths 44 of some or all of the leads 42 are electricallycoupled to the upper microelectronic component 20 by individual wirebonds 24. Similarly, leads 52 of a lower lead frame 50 are physicallyattached to the lower microelectronic component 30 by an adhesive 32.Wire bonds 34 electrically connect the inner lengths 54 of selectedleads 52 to the lower microelectronic component 30. The uppermicroelectronic component 20 and the lower microelectronic component 30may be attached in a variety of ways, such as by a die attach adhesive25.

The microelectronic components 20 and 30 and the inner lengths 44 and 54of the leads 42 and 52, respectively, may be encapsulated in a moldcompound 12. An outer length 46 of each lead 42 of the upper lead frame40 extends outwardly beyond a periphery 14 of the mold compound 12.Similarly, an outer length 56 of each lead 52 of the lower lead frame 50extends outwardly beyond the periphery 14 of the mold compound 12. Theouter lengths 56 of the lower leads 52 may be shaped for connection to asubstrate or another microelectronic component. The TSOP 10 shown inFIGS. 1-5 employs lower leads 52 with generally S-shaped outer lengths,which is commonplace for TSOPs; a wide variety of other shapes are knownin the art for use in different applications.

The upper leads 42 of the TSOP 10 are appreciably shorter than the lowerleads 52. In this design, the upper leads 42 are too short to directlycontact another component, such as a substrate. Instead, the lower leads52 are coupled to the substrate (not shown) and the upper leads 42communicate with the substrate via an electrical connection to the lowerleads 52. As shown in FIG. 3, the leads 42 and 52 may be electricallyconnected using a conventional solder dip process. In such a process,the outer lengths 46 and 56 of the leads 42 and 52, respectively, aredipped in a bath of molten solder. As shown in FIG. 3, to promote anoptimal electrical connection between the upper lead 42 and the lowerlead 52, the solder may cover the entire outer length 46 of the upperlead 42. Unfortunately, current designs tend to require an undue amountof solder to completely cover the outer length 46 of the upper lead 42and to establish consistently reliable electrical connections betweenthe upper lead 42 and lower lead 52 of each vertically superimposed pairof leads (only one pair being shown in FIG. 3).

One factor that may contribute to the need for an excess of solder isthe width of the dam bar used in manufacturing the upper leads 42. FIGS.4 and 5 schematically illustrate aspects of this manufacturing process.As shown in FIG. 4, the lead frame 40 initially includes a dam bar 48that connects the outer lengths 46. In particular, a dam bar element 49is connected to two adjacent leads 42 and spans the space between theouter lengths 46 of the adjacent leads 42. The dam bar 48 (which may beconsidered as comprising the dam bar elements 49 and an outer tipportion of each of the leads 42) both physically supports the outerlengths 46 of the leads 42 during handling and helps block or dam theflow of the mold compound 12 during the molding operation. The dam barelements 49 also electrically short adjacent leads 42 to one another andmust be removed to electrically isolate the upper leads 42 from oneanother. FIG. 5 shows the same package 10 after the dam bar 48 has beentrimmed to remove the dam bar elements 49. Once the dam bar 48 has beentrimmed into the shape shown in FIG. 5, the outer lengths 56 of thelower leads 52 may be formed into the desired shape, e.g., the S shapeshown in FIGS. 2 and 3.

Bending the outer lengths 56 of the lower leads 52 will tend to leave agap 62 between the lower lead 52 and the upper lead 42, as shown in FIG.2. When the leads 42 and 52 are solder-dipped, the solder 60 is expectedto fill this gap 62. The cantilevered distance of the outer length 46extending outwardly above the gap 62 is attributable in large part tothe width W of the dam bar 48. Reducing the width W of the dam bar 48could reduce the size of the gap 62 and the amount of solder 60necessary to fill the gap 62. However, making the dam bar 48 too thincould sacrifice the requisite structural integrity of the lead frame 40,making the lead frame 40 less able to withstand the rigors of normalhandling during manufacture. Making the dam bar 48 thinner may alsocompromise the ability of the dam bar 48 to block the flow of moldcompound during the encapsulation process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a top view of a TSOP microelectronic component package.

FIG. 1B is a side view of the TSOP of FIG. 1A.

FIG. 2 is a schematic end view of the TSOP of FIGS. 1A-B; the dimensionsof the various components have been altered in FIG. 2 to betterillustrate the internal structure of the TSOP.

FIG. 3 is a schematic end isolation view of a pair of leads of the TSOPshown in FIG. 2 after a solder dip process.

FIG. 4 is a schematic top view of a stage in the manufacture of the TSOPof FIGS. 1-3.

FIG. 5 is a schematic top view, similar to FIG. 4, illustrating asubsequent stage in the manufacture of the TSOP of FIGS. 1-3.

FIG. 6 is a top elevation view of a lead frame structure in accordancewith one embodiment of the invention.

FIG. 7 is a schematic top isolation view of a portion of the lead framestructure shown in FIG. 6.

FIG. 8 is a schematic top elevation view of an array of lead sets inaccordance with an embodiment of the invention.

FIG. 9 is a schematic top view illustrating the structure of FIG. 7 in asubsequent stage of manufacture.

FIG. 10 is a schematic end view of a pair of leads in a microelectroniccomponent package in accordance with an embodiment of the invention.

DETAILED DESCRIPTION

A. Overview

Various embodiments of the present invention provide microelectroniccomponent lead frame structures, microelectronic component assemblies,and methods for forming microelectronic component assemblies. The terms“microelectronic component” and “microelectronic component assembly” mayencompass a variety of articles of manufacture, including, e.g., SIMM,DRAM, flash-memory, ASICs, processors, flip chips, ball grid array (BGA)chips, or any of a variety of other types of microelectronic devices orcomponents therefor.

In one embodiment, a microelectronic component lead frame structureincludes a plurality of leads and a plurality of severable dam barelements. Each of the leads has an inner length, and outer length and anouter tip portion. The outer length of each lead is spaced from theouter length of at least one adjacent lead by a lead gap. One of the dambar elements is associated with each lead gap. Each dam bar element isjoined to the outer tip portions of two leads and extends outwardlybeyond the outer ends of the joined outer tip portions.

Another embodiment provides a microelectronic component lead framestructure including a plurality of lead sets arranged in an array. Eachlead set includes a plurality of first leads, a plurality of alignedfirst dam bar elements, a plurality of second leads, and a plurality ofaligned second dam bar elements. Each of the first leads extendsoutwardly in the first direction from an inner length toward an outerlength and an outer tip portion. The outer length of each first lead isspaced from the outer length of at least one adjacent first lead by afirst lead gap. One of the first dam bar elements is associated witheach first lead gap. Each first dam bar element is joined to the outertip portions of two first leads and extends outwardly beyond the outerends of the joined outer tip portions of the first leads. Each of thesecond leads extends outwardly in a second direction from an innerlength toward an outer length and an outer tip portion. The outer lengthof each second lead is spaced from the outer length of at least oneadjacent second lead by a second lead gap. One of the second dam barelements is associated with each second lead gap. Each second dam barelement is joined to the outer tip portions of two second leads andextends outwardly beyond the outer ends of the joined outer tip portionsof the second leads.

A microelectronic component assembly in accordance with anotherembodiment includes a microelectronic component, a plurality of leads,and a plurality of dam bar elements. The microelectronic componentcarries a plurality of contacts. Each of the leads has an inner length,an outer length, and an outer tip portion. The inner lengths of at leastsome of the leads are electrically coupled to one of the contacts andthe outer length of each lead is spaced from the outer length of atleast one adjacent lead by a lead gap. One dam bar element is associatedwith each lead gap. Each dam bar element is joined to the outer tipportions of two leads and extends outwardly beyond the outer ends of thejoined outer tip portions.

In another embodiment, a microelectronic component lead frame structureincludes a set of leads extending in a first direction and a dam bar.Each of the leads has an inner length, an outer length, and an outeredge. The outer lengths are spaced from one another. The dam barcomprises a plurality of dam bar elements. Each dam bar element isjoined to the outer tip portions of two adjacent leads and each dam barelement has an outer edge that extends farther outwardly than the outeredges of the two adjacent leads. The outer edges of the leads and theouter edges of the dam bar elements together define an irregular outeredge of the dam bar.

A microelectronic component lead frame structure of another embodimentcomprises a plurality of leads and a dam bar. Each of the leads extendsoutwardly from an inner length to an outer tip portion. The outer tipportions are spaced from one another by a lead space. The dam barcomprises the outer tip portions of the leads and a plurality of dam barelements. Each dam bar element spans the space between two adjacentouter tip portions. The dam bar has an outer edge that comprises outeredges of the dam bar elements and outer edges of the leads. The outeredge of the dam bar has an inwardly extending recess associated with theouter tip portion of each lead.

Another embodiment of the invention provides a microelectronic componentassembly including a first microelectronic component carrying aplurality of first contacts and a second microelectronic componentcarrying a plurality of second contacts. The microelectronic componentassembly also includes a first lead frame comprising a set of firstleads and a first dam bar. At least some of the first leads areelectrically coupled to one of the first contacts. Each of the firstleads has an outer tip portion spaced outwardly from the firstmicroelectronic component. The first dam bar comprises the outer tipportions of the first leads and a plurality of first dam bar elements.The first dam bar has an irregular outer edge with an inwardly extendingrecess associated with the outer tip portion of each first lead. Themicroelectronic component assembly further includes a second lead framecomprising a set of second leads. At least some of the second leads areelectrically coupled to one of the second contacts. A length of each ofthe second leads is aligned with a length of one of the first leads.Each second lead has an outer length that extends outwardly farther thanthe aligned first lead.

A microelectronic component assembly in accordance with still anotherembodiment includes a first microelectronic component, a secondmicroelectronic component, a plurality of first leads, and a pluralityof second leads. The first microelectronic component carries a pluralityof first contacts and the second microelectronic component carries aplurality of second contacts. The first leads are associated with thefirst microelectronic component and at least some of the first leads areelectrically coupled to one of the first contacts. Each of the firstleads has an outer tip portion spaced outwardly from the firstmicroelectronic component, with each outer tip portion having an outeredge including an inwardly extending recess. The second leads areassociated with the second microelectronic component. At least some ofthe second leads are electrically coupled to one of the second contacts.Each of the second leads is aligned with one of the first leads and hasan outer length that extends outwardly farther than the outer edge ofthe aligned first lead.

A method of assembling a microelectronic component assembly is providedby yet another embodiment. In accordance with this method, a lead frameis positioned with respect to a microelectronic component. The leadframe has a plurality of leads and a dam bar. Each lead may extendoutwardly from an inner length to an outer tip portion that is spacedoutwardly of the microelectronic component. The dam bar may comprise theouter tip portions of the leads and a plurality of dam bar elements,with each dam bar element spanning a space between two adjacent outertip portions. This dam bar may have an outer edge that comprises outeredges of the dam bar elements and outer edges of the leads, with theouter edge of the dam bar having an inwardly extending recess associatedwith the outer tip portion of each lead. At least some of the leads areelectrically coupled to the microelectronic component. Themicroelectronic component and the inner lengths of the leads areencapsulated in a mold compound. The dam bar elements may be trimmed,leaving the leads with the outer tip portions and the inwardly extendingrecess exposed outside the mold compound.

For ease of understanding, the following discussion is subdivided intothree areas of emphasis. The first section discusses certainmicroelectronic component lead frame structures; the second sectionrelates to stacked microelectronic component assemblies in selectembodiments; and the third section outlines methods in accordance withother embodiments of the invention.

B. Microelectronic Component Lead Frame Structures

FIGS. 6-8 illustrate aspects of a lead frame structure 100 in accordancewith one embodiment. The lead frame structure 100 includes a pluralityof leads 110 arranged in a predetermined fashion to achieve the desiredelectrical connectivity with a microelectronic component 150. The leadframe structure 100 may be thought of as including a first bank of leads110 a extending outwardly from the microelectronic component 150 in afirst direction toward a first dam bar 130 a and a second bank of leads110 b extending in a second, generally opposite, direction from themicroelectronic component 150 to a second dam bar 130 b. For purposes ofthe following discussion, the structure of the leads 110 a in the firstbank and 110 b in the second bank may be substantially the same. Hence,in most of the following discussion and in FIGS. 7-10, the leads will begenerally referred to by the reference number 110 and the dam bars willbe generally referred to by the reference number 130.

Each of the leads 110 includes an inner length 112 (112 a-b in FIG. 6),an outer length 114, and an outer tip portion 116. The inner lengths 112of the leads 110 may be electrically coupled to contacts 152 of themicroelectronic component 150 by the plurality of wire bonds 154. Themicroelectronic component 150 may comprise a semiconductor die, forexample, with a row of bond pads aligned down a center line to define arow of contacts 152. If so desired, each of the leads 110 may beelectrically connected to one or more contacts 152. As suggested in FIG.6, though, it is anticipated that, in some embodiments, a number of theleads 110 will not be electrically coupled to the microelectroniccomponent 150. The inner lengths 112 of these leads 110 may still bephysically supported by the microelectronic component, e.g., byemploying a conventional adhesive lead-on-chip tape.

As shown in FIG. 7, the outer lengths 114 of the leads 110 may begenerally parallel to one another and spaced from one another by a leadgap 125. In the illustrated embodiment, the outer lengths 114 of theleads 110 are spaced a fixed distance from one another, yielding auniform lead gap 125 between the pairs of adjacent outer lengths 114.The dam bar 130 generally comprises a plurality of dam bar elements 134and the outer tip portions 116 of the leads 110. Each dam bar element134 spans a lead gap 125 between an adjacent pair of lead outer lengths114. In particular, each dam bar element 134 is joined at a firstlongitudinal end to a side of the outer tip portion 116 of one lead 110and is joined at a second longitudinal end to a side of the outer tipportion 116 of another lead 110. The dam bar elements 134 may be joinedto the adjacent outer tip portions 116 in any desired fashion. In oneembodiment, the dam bar elements 134 and the leads 110 are allintegrally formed from a single sheet of metal foil, e.g., a sheet ofcopper, aluminum, alloy 42, or other metals (e.g., metal alloys) wereknown in the field. Other conventional lead frame materials may be usedinstead of such a metal foil. The lead frame structure 100 may be formedin any suitable fashion, such as by a stamping process or usingphotolithographic etching.

The outer tip portion 116 of each lead 110 includes an outer edge 118.Similarly, each dam bar element 134 has an outer edge 135. The outeredges 118 and 135 together define an outer edge 132 of the dam bar 130.This outer edge 132 may take any of a variety of shapes. In oneembodiment, the outer edge 118 of each outer tip portion 116 includes aninwardly extending recess 120. In the embodiment shown in FIGS. 6 and 7,each of the recesses 120 comprises a concave arc having a radius R₁.This radius R₁ may be varied as desired and the position of the centerof the arc may be selected to yield a recess 120 having the desiredwidth and depth. In one particular embodiment wherein the outer length114 of each of the leads 110 has a width of about 0.32 millimeters, theradius R₁ of the recess may be on the order of about 0.1 millimeters.Although the lead frame structure 100 shown in FIGS. 6 and 7 employslead outer edges 118 with a circular arc recess 120, the recesses 120are not limited to this shape. Square, V-shaped, and ellipticalrecesses, for example, may also suffice.

The position of the recess 120 along the length of the outer edge 118may be varied. In the illustrated embodiment, each of the recesses 120is generally centered about the midline M of the outer length 114 of theassociated lead 110. As a consequence, each recess 120 curves inwardlyfrom a location adjacent to each of the adjoining dam bar elements 134toward the midline M of the outer tip portion 116. This increases thewidth of the dam bar 130 where the dam bar elements 134 are joined tothe leads 110, but reduces the total length of the lead outer lengths114.

The outer edge 135 of each dam bar element 134 may take on any suitableshape. In one embodiment, the outer edges 135 are substantiallystraight, yielding a dam bar 130 having an irregular outer edge 132 thatis generally straight, but is punctuated with a recess 120 associatedwith each lead outer length 114. In the illustrated embodiment, however,the outer edge 135 of each dam bar element 134 is curved. In particular,the outer edges 135 are circular arcs having a radius R₂. This radius R₂is greater than the radius R₁, yielding a dam bar element outer edge 135that curves more gradually than does the recess 120 in the lead outeredge 118. In other embodiments, these two radii R₁ and R₂ may besubstantially the same or the radius R₁ of the recess 120 may be greaterthan the radius of curvature R₂ of the dam bar element outer edge 135.

Whereas the recesses 120 in the lead outer edges 118 are convex,inwardly extending arcs, the outer edge 135 of each dam bar element 134in FIGS. 6 and 7 extends farther outwardly (i.e., to the right in FIG.7) than the outer edges 118 of the two adjacent leads 110. If sodesired, the convex curve of each dam bar element outer edge 135 maymerge tangentially into the concave arcuate recess 120 of both of theadjacent lead outer edges 118, as shown. This will yield a dam bar outeredge 132 wherein the outer edge 135 of each dam bar element 134 mergessmoothly and without a sharp discontinuity into an adjacent portion ofthe outer edge 118 of each adjacent outer tip portion 116. Having arelatively smooth, scalloped outer edge 132 as shown avoids sharpdiscontinuities and curvature that may represent points of stressconcentration in the lead frame structure 100. In the illustratedembodiment, the lead outer lengths 114 are spaced regularly, i.e., thelead gap 125 between each adjacent pair of lead outer lengths 114 isconstant. As a result, the dam bar outer edge 132 has a periodic curvestructure, with a minimum of the curve structure associated with theouter edge 118 of each lead 110.

FIG. 6 illustrates one set of leads 110 adapted for use with a singlemicroelectronic component 150. To facilitate holding the lead framestructure 100 during the wire bonding and subsequent encapsulationsteps, the lead frame structure 100 may include a first end member 140 aand a second end member 140 b extending along opposite ends of the setof leads 110. Each of the dam bars 130 a-b may be attached to the firstend member 140 a by a first strap 142 a. Similarly, the opposite end ofeach dam bar 130 a-b may be attached to the second end member 140 b by astrap 142 b. These straps 142 may be severed in a subsequent trimmingoperation, as discussed below. Each of the end members 140 may beprovided with a series of alignment holes 144. As is known in the art,such alignment holes may be useful in properly aligning the lead framestructure 100 for subsequent wire bonding, encapsulation, and trimmingoperations.

In one embodiment, a plurality of such sets of leads are arranged in anarray. One such array is shown schematically in FIG. 8. The lead framestructure 100 shown in FIG. 8 comprises a linear array with adjacentlead sets (shown schematically as boxes 102 in FIG. 8) positioned sideby side. The first end member 140 a may extend laterally along one edgeof each of the lead sets 102 while the second end member 140 b mayextend laterally along the opposite edge of each lead set 102. Othernonlinear arrays, such as square or rectangular arrays with multiplerows and columns of lead sets 102, may be used instead of the lineararray shown in FIG. 8.

C. Stacked Microelectronic Component Assemblies

FIG. 10 is a fragmentary, schematic end view of a portion of amicroelectronic component assembly 160, and FIGS. 7 and 9 illustratesequential stages in the manufacture of this assembled microelectroniccomponent 160. For the sake of simplicity, most of the elements of themicroelectronic component assembly 160 within the mold compound 162 havebeen omitted from these Figures. It is contemplated that the structurewithin the mold compound 162 may resemble that illustrated in FIG. 2,with a pair of microelectronic components (20 and 30 in FIG. 2) attachedto one another and wire bonded to the inner lengths 112 in FIG. 6 of theleads 110 and inner lengths (not shown) of leads 172 of a second leadframe 170.

As illustrated in FIG. 7, the lower lead frame 170 may have a pluralityof leads 172, each of which has an outer length 174 extending outwardlybeyond the periphery 164 of the mold compound 162. The outer length 174of each of these lower leads 172 may be aligned with the outer length114 of one of the upper leads 110. (Although the leads 110 arecharacterized as “upper” leads and the leads 172 are characterized as“lower” leads, it should be understood that this is merely for purposesof convenience and reflects the orientation of these components asdepicted in FIGS. 7, 9 and 10. Hence, the “lower” leads 172 need not bepositioned vertically beneath the “upper” leads 110, for example.) Theouter length 174 of the lower leads 172 extends outwardly from theperiphery 164 of the mold compound 160 farther than does the outerlength 114 of the upper leads 110. As a consequence, the outer edge 176of each lower lead 172 is spaced outwardly from the mold compound 162farther than the outer edge 118 of the outer tip portion 116 of thealigned upper lead 110. In the illustrated embodiment, the outer edge176 of each lower lead 172 is spaced outwardly farther than any part ofthe outer edge 132 of the dam bar 130 (FIG. 7).

FIG. 9 illustrates the structure of FIG. 7 after the dam bar 130 hasbeen trimmed. In particular, the majority or the entirety of each of thedam bar elements 134 has been trimmed away, physically separating andelectrically isolating each of the upper lead outer lengths 114 from oneanother. Comparing FIG. 9 to FIG. 5 demonstrates that the outer tipportion 116 of leads 110 in FIG. 9 are appreciably shorter than theouter tip portions 46 of the leads 42 in FIG. 5. As a consequence, itwill take less solder to cover the outer tip portions 116 of the leads110 in FIG. 9 than it will to cover the outer tip portions 46 of theleads 42, shown in FIG. 3. This reduced-size outer tip portion can beemployed without unduly sacrificing the structural integrity and dammingfunction of the dam bar 130 by having dam bar elements 134 that extendoutwardly beyond the outer edge 118 of the leads and/or having recesses120 in the outer edges of the leads 110.

In FIGS. 7 and 9, the outer lengths 174 of the lower leads 172 areillustrated as being substantially straight, extending generallyhorizontally outwardly beyond the periphery 164 of the mold compound162. Using conventional forming techniques, the outer lengths 174 of thelower leads 172 may be bent into the desired final shape. If so desired,this may be an S shape as shown in FIG. 10, though other shapes arecertainly possible. If so desired, the outer tip portion 116 of each ofthe upper leads 110 may be bent with the outer lengths 174 of the lowerleads 172 so that the entire length of the outer tip portion 116 liesflush against a surface of the lower lead 172, as shown in FIG. 10.Alternatively, the outer tip portions 116 of the upper leads 110 may beleft as-is without being bent during the forming operation.

In the embodiment shown in FIG. 10, the outer length 174 of the lowerlead 172 has a middle portion that extends substantially vertically inthe orientation shown in FIG. 10. In one embodiment, the outer edges 118of the upper leads 110 extend outwardly beyond the periphery 164 of themold compound 162 a distance no greater than the lateral projection ofthe outer surface of the vertically extending middle portion 173 of thelower lead outer length 174. If so desired, the outer edge 118 of eachof the upper leads 110 may be spaced slightly inwardly from the outersurface of this middle portion 173. In one embodiment, the angle betweenthe outer surface of the middle portion 173 and the outer edge 118 ofthe aligned lead 110, identified in FIG. 10 as angle A, is between about0 degrees and about 5 degrees.

D. Methods

As noted above, certain aspects of the present invention provide methodsfor assembling microelectronic component assemblies. The followingdiscussion of at least one such method refers to the specificembodiments shown in the previous drawings. It should be recognized,however, that this is intended solely to promote understanding and thatany of a variety of other structures may be employed instead.

In assembling a microelectronic component assembly in accordance withone embodiment, a lead frame structure 100 is positioned with respect toa microelectronic component 150. The microelectronic component 150 may,for example, comprise a semiconductor die having a plurality of wirebond pads. At least some of the leads 110 of the lead frame structure100 may be electrically coupled to the microelectronic component 150. Inthe embodiment shown in FIG. 6, this may be accomplished by wire bondingthe inner lengths 112 of selected leads 110 to one or more contacts 152carried by the microelectronic component 150. A second microelectroniccomponent (not shown) may be attached to leads 172 of another lead frame170 in a similar fashion.

The first and second lead frames 100 and 170, respectively, may bejuxtaposed with one another. If so desired, the first and secondmicroelectronic components may be attached to one another, e.g., using adie attach adhesive (shown schematically as reference number 25 in FIG.2). When the first and second lead frames 110 and 170 are juxtaposedwith one another, each of the leads 110 of the first lead frame isjuxtaposed with one of the leads 172 of the second lead frame 170. Inone embodiment, these juxtaposed leads may be in direct physical contactwith one another to enhance electrical connection therebetween.

A portion of the resultant structure can be encapsulated in a moldcompound using conventional molding techniques. The mold compound isformed such that it encapsulates the first and second microelectroniccomponents, the inner lengths 112 of the upper leads 110, and the innerleads (not shown) of the lower leads 172 in the mold compound 162. (Theperiphery of the mold compound 160 is suggested in dashed lines in FIG.6.) This will leave the outer lengths 114 of the upper leads 110 and theouter lengths 174 of the lower leads 172 exposed outside of the moldcompound 162.

Thereafter, the dam bar elements 134 of the upper lead frame 100 may betrimmed, physically separating and electrically isolating the upper leadouter lengths 114 from one another. As shown in FIG. 9, trimming the dambar elements 134 will leave the outer tip portion 116 of each of theupper leads 110 juxtaposed with the outer length 174 of each of thelower leads 172. If so desired, solder may be applied to the outer tipportions 116 of the upper leads 110 and the outer lengths 174 of thelower leads 172, helping to electrically join each upper lead outerlength 114 with the aligned lower lead outer length 174. The solder canbe applied in any desired fashion, e.g., using a solder dip process.

In one adaptation of this method, a plurality of microelectroniccomponents 150 may be attached to sets of leads 102 arranged in anarray, as shown in FIG. 8. If such a structure is employed, the straps142 joining the dam bars 130 to the end members 140 may be severed toseparate the packaged microelectronic component assembly from the endmembers 140. In one embodiment, these straps 142 are severed during thedam bar trim operation.

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense as opposed to anexclusive or exhaustive sense, that is to say, in a sense of “including,but not limited to.” Words using the singular or plural number alsoinclude the plural or singular number, respectively. When the claims usethe word “or” in reference to a list of two or more items, that wordcovers all of the following interpretations of the word: any of theitems in the list, all of the items in the list, and any combination ofthe items in the list.

The above detailed descriptions of embodiments of the invention are notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whilesteps are presented in a given order, alternative embodiments mayperform steps in a different order. The various embodiments describedherein can be combined to provide further embodiments.

In general, the terms used in the following claims should not beconstrued to limit the invention to the specific embodiments disclosedin the specification, unless the above detailed description explicitlydefines such terms. While certain aspects of the invention are presentedbelow in certain claim forms, the inventors contemplate the variousaspects of the invention in any number of claim forms. Accordingly, theinventors reserve the right to add additional claims after filing theapplication to pursue such additional claim forms for other aspects ofthe invention.

1. A microelectronic component lead frame structure, comprising: aplurality of leads, each of which has an inner length, an outer length,and an outer tip portion having a tip outer edge, the outer length ofeach lead being spaced from the outer length of at least one adjacentlead by a lead gap; and a plurality of dam bar elements, one of the dambar elements being associated with each lead gap, each dam bar elementbeing joined to the outer tip portions of two leads and having a dam barouter edge that extends outwardly beyond the tip outer edges of thejoined outer tip portions; wherein the tip outer edges and the dam barouter edges together define a continuous outer edge that includes aplurality of curves.
 2. The microelectronic component lead framestructure of claim 1 wherein each tip outer edge includes an inwardlyextending recess.
 3. The microelectronic component lead frame structureof claim 1 wherein each tip outer edge is curved.
 4. The microelectroniccomponent lead frame structure of claim 1 wherein each tip outer edgecurves inwardly from a location adjacent each adjacent dam bar elementtoward a midline of the outer tip portion.
 5. The microelectroniccomponent lead frame structure of claim 1 wherein each dam bar outeredge merges smoothly into an adjacent portion of the tip outer edge ofeach adjacent outer tip portion.
 6. The microelectronic component leadframe structure of claim 1 wherein the leads and the dam bar elementsare integrally formed of a metal foil.
 7. The microelectronic componentlead frame structure of claim 1 wherein the inner lengths of at leastsome of the leads are electrically coupled to a microelectroniccomponent.
 8. The microelectronic component lead frame structure ofclaim 1 wherein the inner lengths of at least some of the leads areelectrically coupled to a microelectronic component, further comprisinga mold compound encapsulating the microelectronic component and theinner lengths of the leads, the outer tip portions of the leads beingspaced outwardly of the mold compound.
 9. A microelectronic componentlead frame structure, comprising: a plurality of lead sets arranged inan array, each lead set comprising: a plurality of first leads, each ofwhich extends outwardly in a first direction from an inner length towardan outer length and an outer tip portion that has a first tip outeredge, the outer length of each first lead being spaced from the outerlength of at least one adjacent first lead by a first lead gap; aplurality of first dam bar elements, one of the first dam bar elementsbeing associated with each first lead gap, each first dam bar elementbeing joined to the outer tip portions of two first leads and having afirst dam bar outer edge that extends outwardly beyond the tip outerends edges of the joined outer tip portions of the first leads; aplurality of second leads, each of which extends outwardly in a seconddirection from an inner length toward an outer length and an outer tipportion having a second tip outer edge, the outer length of each secondlead being spaced from the outer length of at least one adjacent secondlead by a second lead gap; and a plurality of second dam bar elements,one of the second dam bar elements being associated with each secondlead gap, each second dam bar element being joined to the outer tipportions of two second leads and having a second dam bar outer edge thatextends outwardly beyond the tip outer edges of the joined outer tipportions of the second leads; wherein the first tip outer edges and thefirst dam bar outer edges together define a continuous first outer edge,the second tip outer edges and the second dam bar outer edges togetherdefine a continuous second outer edge, and at least one of the first andsecond outer edges includes a plurality of curves.
 10. Themicroelectronic component lead frame of claim 9 wherein the array of thelead sets comprises a linear array, further comprising a pair of endmembers, each end member extending along an opposite side of the lineararray and being joined to each lead set by at least one strap.
 11. Themicroelectronic component lead frame structure of claim 9 wherein eachof the first and second tip outer edges includes an inwardly extendingrecess.
 12. The microelectronic component lead frame structure of claim9 wherein each of the first and second tip outer edges is curved. 13.The microelectronic component lead frame structure of claim 9 whereineach of the first tip outer edges curves inwardly from a locationadjacent each adjacent dam bar element toward a midline of the outer tipportion.
 14. The microelectronic component lead frame structure of claim9 wherein the first leads, the second leads, the first dam bar elements,and the second dam bar elements are all integrally formed of a metalfoil.
 15. The microelectronic component lead frame structure of claim 9wherein the inner lengths of at least some of the first leads areelectrically coupled to a microelectronic component.
 16. Themicroelectronic component lead frame structure of claim 9 wherein theinner lengths of at least some of the first leads are electricallycoupled to a microelectronic component, further comprising a moldcompound encapsulating the microelectronic component and the innerlengths of the first and second leads, the outer tip portions of thefirst and second leads being spaced outwardly of the mold compound. 17.A microelectronic component assembly comprising: a microelectroniccomponent carrying a plurality of contacts; a plurality of leads, eachof which has an inner length, an outer length, and an outer tip portionhaving a curved outer edge, the inner lengths of at least some of theleads being electrically coupled to one of the contacts and the outerlength of each lead being spaced from the outer length of at least oneadjacent lead by a lead gap; and a plurality of dam bar elements, withone dam bar element associated with each lead gap, each dam bar elementbeing joined to the outer tip portions of two leads and extendingoutwardly beyond the curved outer edges of the joined outer tipportions.
 18. The microelectronic component assembly of claim 17 furthercomprising a mold compound encapsulating the microelectronic componentand the inner lengths of the leads, the outer lengths of the leadsextending outwardly of the mold compound.
 19. The microelectroniccomponent assembly of claim 17 further comprising a mold compoundencapsulating the microelectronic component and the inner lengths of theleads, the outer lengths of the leads extending outwardly of the moldcompound and each of the dam bar elements being spaced from a peripheryof the mold compound.
 20. The microelectronic component assembly ofclaim 17 wherein the curved outer edges define inwardly extendingrecesses.
 21. The microelectronic component assembly of claim 17 whereinthe curved outer edges are curved concavely.
 22. The microelectroniccomponent assembly of claim 17 wherein the curved outer edges curveinwardly from a location adjacent each adjacent dam bar element toward amidline of the outer tip portion.
 23. The microelectronic componentassembly of claim 17 wherein each dam bar element includes an outeredge, the outer edge of each dam bar element merging smoothly into anadjacent portion of the curved outer edge of each adjacent outer tipportion.
 24. The microelectronic component assembly of claim 17 whereinthe leads and the dam bar elements are integrally formed of a metalfoil.
 25. A microelectronic component lead frame structure, comprising:a set of leads extending in a first direction, each of the leads havingan inner length, an outer length, and an outer edge, the outer lengthsbeing spaced from one another; and a dam bar comprising a plurality ofdam bar elements, each dam bar element being joined to the outer lengthsof two adjacent leads and each dam bar element having an outer edge thatextends farther outwardly than the outer edges of the two adjacentleads, the outer edges of the leads and the outer edges of the dam barelements together defining an outer edge of the dam bar that includes aplurality of curves.
 26. The microelectronic component lead framestructure of claim 25 wherein the outer edge of the dam bar has aperiodic curve structure.
 27. The microelectronic component lead framestructure of claim 25 wherein the outer edge of the dam bar has aperiodic curve structure having a minimum associated with the outer edgeof each lead.
 28. The microelectronic component lead frame structure ofclaim 25 wherein the outer edge of each outer tip portion includes aninwardly extending recess.
 29. The microelectronic component lead framestructure of claim 25 wherein the outer edge of each outer tip portionincludes a concave curve.
 30. The microelectronic component lead framestructure of claim 25 wherein the outer edge of each outer tip portioncurves inwardly from a location adjacent each adjacent dam bar elementtoward a midline of the outer tip portion.
 31. The microelectroniccomponent lead frame structure of claim 25 wherein the outer edge ofeach dam bar element merges smoothly into an adjacent portion of theouter edge of each adjacent outer tip portion.
 32. The microelectroniccomponent lead frame structure of claim 25 wherein the leads and the dambar are integrally formed of a metal foil.
 33. The microelectroniccomponent lead frame structure of claim 25 wherein the inner length ofat least some of the leads are electrically coupled to a microelectroniccomponent.
 34. The microelectronic component lead frame structure ofclaim 25 wherein the inner length of at least some of the leads areelectrically coupled to a microelectronic component, further comprisinga mold compound encapsulating the microelectronic component and theinner lengths of the leads, the outer tip portions of the leads beingspaced outwardly of the mold compound.
 35. A microelectronic componentlead frame structure, comprising: a plurality of leads, each of whichextends outwardly from an inner length to an outer tip portion, theouter tip portions being spaced from one another by a lead space; and adam bar comprising the outer tip portions of the leads and a pluralityof dam bar elements, each dam bar element spanning the space between twoadjacent outer tip portions, the dam bar having an outer edge thatcomprises outer edges of the dam bar elements and outer edges of theleads, with the outer edge of the dam bar having a series of inwardlyextending, curved recesses.
 36. The microelectronic component lead framestructure of claim 35 wherein the outer edge of the dam bar has aperiodic curve structure.
 37. The microelectronic component lead framestructure of claim 35 wherein each recess comprises a concave curve. 38.The microelectronic component lead frame structure of claim 35 whereinthe outer edge of each outer tip portion curves inwardly from a locationadjacent each adjacent dam bar element toward a midline of the outer tipportion to define the recess of the outer tip portion.
 39. Themicroelectronic component lead frame structure of claim 35 wherein theouter edge of each dam bar element merges smoothly into an adjacentportion of the outer edge of each adjacent outer tip portion.
 40. Themicroelectronic component lead frame structure of claim 35 wherein theleads and the dam bar are integrally formed of a metal foil.
 41. Themicroelectronic component lead frame structure of claim 35 wherein theinner length of at least some of the leads are electrically coupled to amicroelectronic component.
 42. The microelectronic component lead framestructure of claim 35 wherein the inner length of at least some of theleads are electrically coupled to a microelectronic component, furthercomprising a mold compound encapsulating the microelectronic componentand the inner lengths of the leads, the outer tip portions of the leadsbeing spaced outwardly of the mold compound.